Adjustable exhaust snout for outboard motors



April 1962 E. c. KIEKHAEFER 3,029,769

ADJUSTABLE EXHAUST SNOUT FOR OUTBOARD MOTORS Filed Feb. 13, 1961 INVENTOR. ELMER C. KIEKHAEFER BY WWW ATTORNEYS United States Patent 3,629,769 ADJUSTABLE EXHAUST SNGUT FOR OUTBOARD MOTORS Elmer Carl Kielthaefer, Elm Grove, Wis., assignor, by mesne assignments, to Kiekhaefer Corporation, Chicago, 111., a corporation of Delaware Filed Feb. 13, 1961, Ser. No. 89,061 2 Claims. (Cl. 115-48) This invention relates generally to outboard motors of the propeller driven type and more particularly to the exhaust snout therefor.

Outboard motors are mounted on the boat about a generally vertical axis and steering of the boat is effected by pivoting the-motor about this axis. In operation, the propeller creates an undesirable steering torque on the motor which tends to rotate the latter about this vertical axis. This torque is present whether the propeller is fully submerged or only partially submerged. The exact cause of this torque is not entirely clear, but is thought to result from the fact that the propeller blade nearest the surface of the Water exerts less force than the deeper blade. Consequently the lateral force exerted by the lower blade tends to turn the motor. It is thought the lower blade may create more force, because the heavy strut section of the lower gearcase shields the upper blades, that is, it blocks off a portion of the water flow past the upper blade. On the other hand, the very thin skeg below the horizontal center line of the propeller shaft permits full flow of the water to reach the lower propeller blade.

Another reason for unequal propeller blade force, which is thought to contribute to this undesirable steering torque, is that the propeller in the upper position is more likely to be affected by the adjacent Water surface and the flow pattern in that vicinity can be disturbed.

In any event, this propeller steering torque has presented problems to the efiicient operation of an outboard motor. As a result of this steering action of the propeller,

the operator must continually apply a counter-balancing torque in order to keep the boat on its intended course. Stated otherwise, he must maintain a counter-balancing torque on the steering apparatus, the amount of which varies with the boat speed.

In accordance with the present invention, an underwater exhaust snout and the exhaust discharging therefrom are utilized to counter-balance the propeller torque in the operation of a propeller driven outboard motor.

More specifically, an outboard motor mounted on a generally vertical steering axis and having a rotatably driven propeller which creates a torque force tending to turn the motor on its steering axis, is provided with underwater exhaust means having a discharge snout disposed at an angle to the direction of travel so that the hydrodynamic reaction force of the water on the snout together with the lateral thrust force component of the discharging exhaust tend to compensate for the steering torque force of the propeller.

Other objects and advantages will appear more fully hereinafter as this disclosure progresses, reference being had to the accompanying drawings in which:

FIG. 1 is a side elevational view of an outboard motor embodying the presentinvention;

FIG. 2 is a fragmentary bottom view of the motor shown in FIG. 1; and

FIG. 3 is a fragmentary, elevational, enlarged crosssectional view showing the adjustable connection of the snout to the anti-cavitation plate of the motor.

Referring to the drawings, the outboard motor unit comprises a clamp bracket assembly which is adapted to be secured to the transom of a boat. The driveshaft housing 11 is pivotally mounted on the vertical swivel 3,029,769 Patented Apr. 17, 1952 ice pin 12 to the clamp bracket assembly and steering of the boat is effected in the Well-known manner by swinging the motor about this vertical pivot.

Rotation of the propeller 14 creates a torque force on the part of the outboard unit that is. pivoted on the swivel pin 12, and this torque causes the motor unit to swing in one direction about this vertical pivot 12. More particularly, with the propeller pitched as shown and rotating as indicated, the torque created by the propeller tends to rotate the motor unit in the direction shown by the curvilinear arrow T in FIGURE 2. This torque increases with an increase in propeller speed and as a result, the operator must continually apply a counterbalancing steering force in order to keep the boat on the desired course. This constant attention required of the operator is not only fatiguing to him, but the resulting inherent tendency of the boat to circle is somewhat dangerous because of the possibility of the boat overturning in the event of momentary operator inattentiveness.

The exhaust of the motor is directed in a rearwardly direction through the exhaust snout 19 which extends beneath the anti-cavitation plate 15.

In accordance with the present invention the exhaust snout is directed at an angle to the direction of boat travel so that the slipstream water diverted by the angularly disposed snout together with the lateral thrust force component of the discharging exhaust create a torque which is in opposition to the torque T developed by propeller rotation.

The snout is adjustably secured to the plate 15 as follows, reference'being had to FIG. 3. .The anticavitation plate 15 is provided with a counterbore 16 having a tapped hole 17 rearwardly thereof, and an arcuate slot 18 forwardly thereof.

The adjustable snout 19 is preferably formed from a die-cast aluminum alloy and comprises a round plate section 20 which is adapted to be rotatably seated in the counterbore 16. An aperture 21 forwardly of the plate 20 registers with the slot 13 in the anti-cavitation plate and a slot 22 rearwardly of the plate 20 registers with the anti-cavitation plate aperture 17. A cap bolt 23 passes through slot 22 and is threadably engaged in aperture 17 to adjustably secure the snout rearwardly. A bevel headed bolt 24 passes through aperture 21 and slot 18 and a nut 25 holds it captive therein and is itself prevented from turning by the adjacent engaging shoulder 26 formed integrally with the anti-cavitation plate. By this adjustable connection, the snout may be angularly set for the desired operating speed.

The exhaust opening 28 rearwardly of the snout 19 is vertically elongated and converges in a downwardly direction. The leading edge 3%) of the snout is closed and cgpaprises generally a knife-like edge which together with the triangularly-shaped relatively flat sides 31, serves as a very effective trim tab.

The angularity of the snout 19 with respect to the direction of travel gives rise to a hydrodynamic reaction force of the water on the snout and a lateral thrust force component by the discharging exhaust which together produce the torque T about the swivel pin 12 in opposition to the propeller torque T as noted in FIGURE 2. The angle of the snout may be adjusted and locked in a given position to produce a magnitude of torque T to more accurately counterbalance the torque T for any desired boat speed. For a given boat speed the angle will vary, of course, depending on engine size, boat size and types and other factors. A range of twelve degrees from either side of the longitudinal centerline of the boat has been found satisfactory, however, for a majority of situations, but the invention should not,

of course, be limited to any range of angularity of the snout.

By being able to ofi'set the snout in either direction from the longitudinal centerline, matched pairs of engines with propellers rotating in opposite directions may be utilized in a single boat installation.

By combining the functions of the exhaust snout with that of a trim tab, lower overall drag is imposed on the motor unit than when using separate exhaust snout and trim tabs.

This application is a continuation-impart of applicants copending application, Serial No. 695,296, filed November 8, 1957, now abandoned, and entitled Adjustable Exhaust Snoutfor Outboard Motors.

Various modes of carrying out the invention are contemplated as being Within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. In an outboard motor mounted on a generally 20 vertical steering axis and having a rotatably driven underwater propeller which creates a torque force tending to turn the motor on said steering axis, underwater exhaust means for said motor having a discharge snout disposed at an angle to the direction or travel to provide a lateral thrust component force by the discharging exhaust tending to compensate for said steering torque force of said propeller.

2. The construction of claim 1 in which said snout is adjustable in direction to vary the lateral thrust direction of the exhaust.

References Cited in the file of this patent UNITED STATES PATENTS 1,716,962 Johnson June 11, 1929 1,980,685 Johnson Nov. 13, 1934 2,224,900 Conover Dec. 17, 1940 

